This invention relates to apparatus detecting the presence and location of a conductor which extends on opposite sides of an air/water boundary, for example in the case of a command control wire leading from a location on a bank of a body of water to an explosive mine situated under the water. More particularly, the invention is directed to an improved, towable detector device for use in such systems that rely upon operation of the wire to be detected as an antenna. As is discussed in my copending Pat. application Ser. No. 354,560, filed Apr. 20, 1973, and assigned to the assignee hereof, radio broadcast signals are readily picked up by the above water portion of the wire and retransmitted by the underwater portion. An antenna coil, connected to a radio receiver and towed underwater so as to come into close proximity to the wire, serves as a detector of the retransmitted radio waves and hence of the wire. When the water concerned is salt or brackish the radio waves from the primary transmitter are sufficiently attenuated to prevent their interference with, or masking of, the reception of the secondary transmissions from the wire. That is to say the salt or brackish water serves as a radio frequency shield for the detector. Now, since the attenuation is a function of water depth and the electrical conductivity of the water, the shielding effect of fresh water has been found to be insufficient in some circumstances to prevent masking of or interference with the retransmitted signals with resulting loss of ability to accurately detect the presence of the wire.
Moreover, detectors used heretofore have generally required a specific orientation of the towed body in order to maintain the detector coil or antenna in its most sensitive attitude relative to a wire lying on a substantially horizontal bottom surface. To accomplish this, various wing or vane configurations have been provided on the towed detector body. While these have been of considerable use, they have at times become inverted and required time consuming retrieval and righting procedures, and have generally made the towed body difficult to handle, subject to snags, and the like.